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Versions: 00 01

XCON Working Group                                              B. Rosen
Internet-Draft                                                   Marconi
Expires: January 14, 2005                                    A. Johnston
                                                                     MCI
                                                           July 16, 2004


             SIP Conferencing: Sub-conferences and Sidebars
                   draft-rosen-xcon-conf-sidebars-01

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   RFC 3668.

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   This Internet-Draft will expire on January 14, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This document discusses the creation, management of operation of
   sub-conferences in a centralized conferencing architecture, also
   known as "sidebars".  This work uses the SIP Conferencing Framework
   and builds on the descriptions of sub-conferences in that document.
   Examples of SIP and XCON protocols are given.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Sidebars and Dialogs . . . . . . . . . . . . . . . . . . . . .  3
   3.  Sidebar mechanism requirements . . . . . . . . . . . . . . . .  4
   4.  Creating Sidebars  . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Adding Participants to a Sidebar . . . . . . . . . . . . . . .  7
   6.  Terminating a Sidebar  . . . . . . . . . . . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   9.1   Normative References . . . . . . . . . . . . . . . . . . . . 12
   9.2   Informative References . . . . . . . . . . . . . . . . . . . 13
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
       Intellectual Property and Copyright Statements . . . . . . . . 15




































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1.  Introduction

   This document uses the concepts and definitions from the SIP high
   level conferencing requirements and the SIP conferencing framework
   [9] documents.

   While the SIP conferencing framework document describes both SIP and
   XCON methods for creating and managing a centralized conference, this
   document will assume a non-SIP method, as sidebars are an advanced
   conferencing application.  Examples of the non-SIP methods include
   the XCON protocols (used as examples) an  IVR, or a web page.

2.  Sidebars and Dialogs

   Conference establishment using SIP dialogs is described in the SIP
   conferencing framework document.  The set of XCON protocols to also
   establish a conference is currently being developed and designed by
   the XCON working group.  Since the details are TBD, this document
   will refer to the protocol as CPCP (Conference Policy Control
   Protocol) [8] and omit the details of the messages until they are
   developed.

   In SIP sessions, it is not uncommon to have a single dialog with
   multiple media sessions.  The SIP Conferencing Framework assumes this
   - that a participant uses the Conference URI to establish an INVITE
   dialog that results in the establishment of one or more media
   streams.  Media streams established using separate dialogs are
   usually assumed to be unrelated.  For example, a pair of SIP/PSTN
   gateways may have a number of dialogs established between them, and
   the resulting media streams represent separate calls or sessions.

   As a result, the simplest sidebar dialog model is to reuse the
   existing main conference dialog to establish the sidebar.  This has
   the advantage of allowing even the simplest endpoints which are
   incapable of any local mixing to participate in a conference with
   sidebars, provided a non-SIP method of controlling the conference is
   provided.

   It is also possible for a sidebar to have a separate dialog.
   However, the motivation and advantages for this are not obvious.  As
   a result, this document will be restricted to the case of a single
   dialog and the reuse of that dialog for sidebars.

   As discussed in the framework, a sub-conference is identified by a
   URI.  This URI is an alias for the main conference - that is, it must
   resolve to the same focus as the main conference.  If an intended
   sidebar participant is not a participant in the main conference, the
   intended participant joins the conference using the sidebar URI using



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   normal SIP means and is added into the sidebar only.  If that
   participant wishes to become part of the main conference, either a
   re-INVITE with the main conference URI in the Contact is used, or an
   INVITE with Replaces from the main conference is issued.  Of course,
   if the participant wishes to maintain separate dialogs, a simple new
   INVITE would be sent to/from the main conference URI.

3.  Sidebar mechanism requirements

   A properly authorized participant in a conference which allows
   sidebars must be able to:

   REQ-1 Create a sidebar conference.

   REQ-2 Invite participants to join the sidebar, both members of the
   main conference and outside the conference.

   REQ-3 Discover the status of the invited participants.

   REQ-4 Remove participants from a sidebar.

   REQ-5 Delete the sidebar.

   In addition, any participant or potential participant in a sidebar
   must be able to:

   REQ-6 Discover they have been invited to a sidebar.

   REQ-7 Accept or deny an invitation to a sidebar.

   REQ-8 Discover who else is a participant in the sidebar.

   REQ-9 Switch back and forth between the sidebar and the main
   conference.

   REQ-10 Add/delete media streams in the sidebar.

   REQ-11 Leave the sidebar.

   CPCP [8] can meet requirements REQ-1, REQ-2, REQ-5, REQ-6, and
   REQ-10.

   As the conference package [5] contains sidebar rosters, notifications
   from the focus can meet requirements REQ-3 and REQ-8.  In addition,
   if a "pending" user status is added to the conference package (or the
   existing "on-hold" status reused), it can meet requirement REQ-6.

   The remaining requirements need to be met using controls provided by



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   the template, as discussed in the media policy document.
   Specifically, REQ-9 is needed if the nature of the media type limits
   the user to participation in only one stream at a time.  For example,
   a user can effectively only listen to a single audio stream at a
   time, so they can only participate in either the main audio
   conference or in an audio sidebar but not both at the same time.  On
   the other hand, a user can easily participate in multiple text
   sidebars while still participating actively in the main conference.
   Thus, the need for this requirement is media specific.

   In the main conference, the equivalent requirements to requirements
   REQ-7, REQ-9 and REQ-11 are met using the signaling protocol, i.e.
   an INVITE is accepted or rejected to join the main conference, a
   re-INVITE places media streams on and off hold, and a BYE is sent to
   leave the main conference.  Since a sidebar shares the main
   conference dialog, clearly these signaling methods are not
   applicable, except for a participant who is only in the sidebar and
   not a participant in the main conference.  However, the signaling
   could still be used as the channel to convey this information.  For
   example, a re-INVITE could be initiated by the participant to accept
   the sidebar invitation if an SDP attribute were defined to convey
   this information.  A re-INVITE could also be used to switch between
   participation in the main conference and the sidebar, and to leave
   the sidebar.

   Alternatively, a CPCP command could be used meet REQ-7, REQ-9 and
   REQ-11.

   Until one approach or the other is chosen for this, the call flows
   will show CPCP/re-INVITE as the mechanism for accepting or denying a
   sidebar invitation.  switching between participation in the main
   conference and the sidebar, and leaving a sidebar.

4.  Creating Sidebars

   The SIP conferencing architecture supports multiple media types and
   both centralized and distributed mixing.  Sidebars also have this
   same property.  The media type and mixing mode of a sidebar need not
   be the same as the main conference.

   In the simplest case, the sidebar has the same media types as the
   main conference, and is centrally mixed.  In this case, the focus
   changes the mix for the sidebar participants, and no SIP signaling is
   necessary - the existing main conference mix is replaced with the
   sidebar mix.

   On the other hand, if the sidebar has different media types than the
   main conference, then the focus will need to re-INVITE, adding the



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   new media stream(s).  Conference package notifications and SDP
   information will be used by the User Agent to render the new media
   stream in the proper context as a sidebar.

   For fully distributed mixing of single dialog sidebars, the focus may
   need to re-INVITE to add a media stream if the media stream is not
   already being sent to the participant.  The participant will be
   notified of the desired mix using a non-SIP protocol which will
   result in the creation of the sidebar.

   Figure 1 shows a call flow for the creation of a sidebar conference.
   In this flow and those that follow, Alice, Bob, and Carol are
   participants in the main conference while Devon is not.






































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    Alice                Focus                 Carol                 Bob
       |                    |                    |                    |
       |<==================>|                    |                    |
       |                    |<==================>|                    |
       |                    |<=======================================>|
       |                    |                    |                    |
       |              Alice creates a sidebar using CPCP.             |
       |                    |                    |                    |
       | CPCP Create Sidebar F1                  |                    |
       |------------------->|                    |                    |
       | CPCP Acknowledgement F2                 |                    |
       |<-------------------|                    |                    |
       |                    |                    |                    |
       |       Alice adds herself into the sidebar using CPCP.        |
       |                    |                    |                    |
       | CPCP Add Alice to sidebar F3            |                    |
       |------------------->|                    |                    |
       | CPCP Acknowledgement F4                 |                    |
       |<-------------------|                    |                    |
       |                    |                    |                    |
       |       Alice is notified that she is invited to the sidebar   |
       |                    |                    |                    |
       |     NOTIFY F5      |                    |                    |
       |<-------------------|                    |                    |
       |     200 OK F6      |                    |                    |
       |------------------->|                    |                    |
       |                    |                    |                    |
       |       Alice joins the sidebar           |                    |
       |                    |                    |                    |
       | CPCP/re-INVITE F7  |                    |                    |
       |<------------------>|                    |                    |
       |                    |                    |                    |
       |  Alice is notified that she is a participant in the sidebar  |
       |                    |                    |                    |
       |     NOTIFY F8      |                    |                    |
       |<-------------------|                    |                    |
       |     200 OK F9      |                    |                    |
       |------------------->|                    |                    |
   Figure 1. Creation of a Sidebar.


5.  Adding Participants to a Sidebar

   Participants can be added to a sidebar in a number of ways.  If the
   intended sidebar participant is already a participant in the main
   conference and desires a single dialog, then some non-SIP means will
   be used to add the participant.




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   On the other hand, if the participant is not in the main conference,
   a SIP means such as a REFER with the Refer-To URI set to the sidebar
   URI can be used, or a non-SIP means.  Either way, a new dialog will
   be established with the participant and they will join the sidebar
   using some non-SIP means.

    Alice                Focus                 Carol                 Bob
       |                    |                    |                    |
       |<==================>|                    |                    |
       |                    |<==================>|                    |
       |                    |<=======================================>|
       |                    |                    |                    |
       |         Alice adds Carol to the sidebar using CPCP           |
       |                    |                    |                    |
       | CPCP Add Carol to sidebar F1            |                    |
       |------------------->|                    |                    |
       | CPCP Acknowledgement F2                 |                    |
       |<-------------------|                    |                    |
       |                    |                    |                    |
       |  Carol is notified that she has been invited to the sidebar with Alice
       |                    |                    |                    |
       |                    |      NOTIFY F3     |                    |
       |                    |------------------->|                    |
       |                    |      200 OK F4     |                    |
       |                    |<-------------------|                    |
       |                    |                    |                    |
       |               Carol joins the sidebar   |                    |
       |                    |                    |                    |
       |                    |  CPCP/re-INVITE F5 |                    |
       |                    |<------------------>|                    |
       |                    |                    |                    |
       |     Alice is notified that Carol has joined the sidebar      |
       |                    |                    |                    |
       |     NOTIFY F6      |                    |                    |
       |<-------------------|                    |                    |
       |      200 OK F7     |                    |                    |
       |------------------->|                    |                    |
       |                    |                    |                    |
       |        Carol is notified that she is now in the sidebar      |
       |                    |                    |                    |
       |                    |     NOTIFY F8      |                    |
       |                    |------------------->|                    |
       |                    |     200 OK F9      |                    |
       |                    |<-------------------|                    |


   Figure 2. Adding a participant to a sidebar.




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    Alice                Focus                 Carol               Devon
       |                    |                    |                    |
       |<==================>|                    |                    |
       |                    |<==================>|                    |
       |                    |                                         |
       | Alice adds Devon who is not in the conference to the sidebar.|
       |                    |                                         |
       | CPCP Add Devon to sidebar F1                                 |
       |------------------->|                                         |
       | CPCP Acknowledgement F2                                      |
       |<-------------------|                                         |
       |                    |                                         |
       |      Alice sends a REFER to Devon to join to the sidebar     |
       |                    |                                         |
       |               REFER Refer-To:sip:Sidebar-ID F3               |
       |------------------------------------------------------------->|
       |                    202 Accepted F4                           |
       |<-------------------------------------------------------------|
       |                    |     NOTIFY F5                           |
       |<-------------------------------------------------------------|
       |                    |     200 OK F6                           |
       |------------------------------------------------------------->|
       |                    |           INVITE sip:Sidebar-ID F7      |
       |                    |<----------------------------------------|
       |                    |               180 Ringing F8            |
       |                    |---------------------------------------->|
       |                    | 200 OK Contact:sip:Sidebar-ID;isfocus F9|
       |                    |---------------------------------------->|
       |                    |                   ACK F10               |
       |                    |<----------------------------------------|
       |                    |                    RTP                  |
       |                    |<=======================================>|
       |                    |         SUBSCRIBE sip:Sidebar-ID F11    |
       |                    |<----------------------------------------|
       |                    |                  200 OK F12             |
       |                    |---------------------------------------->|
       |                    |                                         |
       | Devon is notified that she has been invited to a sidebar with Alice
       |                    |                                         |
       |                    |                NOTIFY F13               |
       |                    |---------------------------------------->|
       |                    |                200 OK F14               |
       |                    |<----------------------------------------|
       |                    |                                         |
       |                    |        Devon joins the sidebar          |
       |                    |                                         |
       |                    |           CPCP/re-INVITE F15            |
       |                    |<--------------------------------------->|



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       |                    |                                         |
       |    Devon is notified that Alice is in the sidebar with her   |
       |                    |                                         |
       |                    |                NOTIFY F16               |
       |                    |---------------------------------------->|
       |                    |                200 OK F17               |
       |                    |<----------------------------------------|
       |                    |                                         |
       |      Alice is notified that Devon has joined the sidebar     |
       |                    |                                         |
       |     NOTIFY F18     |                                         |
       |<-------------------|                                         |
       |      200 OK F19    |                                         |
       |------------------->|                                         |
       |                    |                    |                    |
       |        Carol is notified that Devon has joined the sidebar   |
       |                    |                    |                    |
       |                    |     NOTIFY F20     |                    |
       |                    |------------------->|                    |
       |                    |     200 OK F21     |                    |
       |                    |<-------------------|                    |

   Figure 3. Adding a participant to a sidebar who is not a member of the
   main conference.


6.  Terminating a Sidebar

   Participation in a single dialog sidebar is terminated by non-SIP
   means.  When the last participant leaves it, the sidebar ceases to
   exist.  A multiple dialog sidebar is terminated by a BYE on the
   dialog for each of the participants.  When the last participant
   leaves it, the sidebar ceases to exist, and the sidebar URI becomes
   unusable.  Note that a single participant sidebar is permissible -
   another participant may join later.

    Alice                Focus                 Carol                Devon
       |                    |                    |                    |
       |<==================>|                    |                    |
       |                    |<==================>|                    |
       |                    |<=======================================>|
       |                    |                    |                    |
       |                   Carol leaves the sidebar.                  |
       |                    |                    |                    |
       |                    |  CPCP/re-INVITE F1 |                    |
       |                    |<------------------>|                    |
       |                    |                    |                    |
       |        Carol is notified that she has left the sidebar       |



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       |                    |                    |                    |
       |                    |     NOTIFY F2      |                    |
       |                    |------------------->|                    |
       |                    |     200 OK F3      |                    |
       |                    |<-------------------|                    |
       |                    |                                         |
       |    Devon is notified that Carol has left the sidebar         |
       |                    |                                         |
       |                    |                NOTIFY F4                |
       |                    |---------------------------------------->|
       |                    |                200 OK F5                |
       |                    |<----------------------------------------|
       |                    |                                         |
       |      Alice is notified that Carol has left the sidebar       |
       |                    |                                         |
       |     NOTIFY F6      |                                         |
       |<-------------------|                                         |
       |     200 OK F7      |                                         |
       |------------------->|                                         |
       |                    |        Devon leaves the sidebar.        |
       |                    |                                         |
       |                    |                BYE F8                   |
       |                    |<----------------------------------------|
       |                    |               200 OK F9                 |
       |                    |---------------------------------------->|
       |                    |                                         |
       |        Devon is notified that she has left the sidebar.      |
       |                    |                                         |
       |                    |                NOTIFY F10               |
       |                    |---------------------------------------->|
       |                    |                200 OK F11               |
       |                    |<----------------------------------------|
       |                    |
       |        Alice is notified that Devon has left the sidebar.
       |                    |
       |     NOTIFY F12     |
       |<-------------------|
       |     200 OK F13     |
       |------------------->|
       |                    |
       | Alice leaves the sidebar.
       |                    |
       | CPCP/re-INVITE F14 |
       |<------------------>|
       |                    |
       |      Alice is notified that she has left the sidebar.
       |                    |
       |     NOTIFY F15     |



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       |<-------------------|
       |     200 OK F16     |
       |------------------->|

   Figure 4. Terminating a sidebar.


7.  Security Considerations

   This document discusses call control for SIP conferencing.  Both call
   control and conferencing have specific security requirements which
   will be summarized here.  Conferences generally have authorization
   rules about who may or may not join a conference, what type of media
   may or may not be used, etc.  This information is used by the focus
   to admit or deny participation in a conference.  It is recommended
   that these types of authorization rules be used to provide security
   for a SIP conference.  For this authorization information to be used,
   the focus needs to be able to authenticate potential participants.
   Normal SIP identity mechanisms including Digest challenge,
   certificates, and identity header fields can be used.  These
   conference specific security requirements are discussed further in
   the requirements and framework documents.

   For call control security, a user agent must maintain local policy on
   who is permitted to perform call control operations, initiate REFERs,
   and replace dialogs.  Normal SIP authentication mechanisms are also
   appropriate here.  The specific authentication and authorization
   schemes are described in the multiparty call control framework
   document.

8.  IANA Considerations

   None.

9.  References

9.1  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [3]  Sparks, R., "The Session Initiation Protocol (SIP) Refer
        Method", RFC 3515, April 2003.




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   [4]  Roach, A., "Session Initiation Protocol (SIP)-Specific Event
        Notification", RFC 3265, June 2002.

   [5]  Rosenberg, J. and H. Schulzrinne, "A Session Initiation Protocol
        (SIP) Event Package for Conference State",
        draft-ietf-sipping-conference-package-04 (work in progress), May
        2004.

   [6]  Mahy, R. and D. Petrie, "The Session Inititation Protocol (SIP)
        'Join' Header", draft-ietf-sip-join-03 (work in progress),
        February 2004.

   [7]  Rosenberg, J., "Indicating User Agent Capabilities in the
        Session Initiation Protocol  (SIP)",
        draft-ietf-sip-callee-caps-03 (work in progress), January 2004.

   [8]  Khartabil, H. and P. Koskelainen, "The Conference Policy Control
        Protocol (CPCP)", draft-ietf-xcon-cpcp-xcap-00 (work in
        progress), May 2004.

9.2  Informative References

   [9]   Rosenberg, J., "A Framework for Conferencing with the Session
         Initiation Protocol",
         draft-ietf-sipping-conferencing-framework-02 (work in
         progress), June 2004.

   [10]  Campbell, B. and R. Sparks, "Control of Service Context using
         SIP Request-URI", RFC 3087, April 2001.

   [11]  Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
         November 2002.

   [12]  Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K.
         Summers, "Session Initiation Protocol (SIP) Basic Call Flow
         Examples", BCP 75, RFC 3665, December 2003.


Authors' Addresses

   Brian Rosen
   Marconi
   1000 FORE Drive
   Warrendale, PA  15086

   EMail: brian.rosen@marconi.com





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   Alan Johnston
   MCI
   100 South 4th Street
   St. Louis, MO  63102

   EMail: alan.johnston@mci.com













































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